diff --git a/frontend/src/lib/components/Editor.svelte b/frontend/src/lib/components/Editor.svelte
index 6f1e2c222c..f050c8d1f3 100644
--- a/frontend/src/lib/components/Editor.svelte
+++ b/frontend/src/lib/components/Editor.svelte
@@ -107,7 +107,7 @@
 	} from './lint/typescriptExtraLibs'
 	import { createWindmillAta, genAtaRoot } from './lint/typescriptAta'
 	import { readModelMarkers } from './lint/markers'
-	import { buildDenoImportMap, lspServersFor } from './lint/lspLanguageConfig'
+	import { buildDenoImportMap, hasLanguageServers, lspServersFor } from './lint/lspLanguageConfig'
 	import { aiChatManager } from './copilot/chat/AIChatManager.svelte'
 	import type { Selection } from 'monaco-editor'
 	import { canHavePreprocessor, getPreprocessorModuleCode } from '$lib/script_helpers'
@@ -980,15 +980,7 @@
 	export async function reloadWebsocket() {
 		await closeWebsockets()
 
-		if (
-			!useWebsockets ||
-			!(
-				(lang == 'typescript' && scriptLang === 'deno') ||
-				lang == 'python' ||
-				lang == 'go' ||
-				lang == 'shell'
-			)
-		) {
+		if (!useWebsockets || !hasLanguageServers(lang, scriptLang)) {
 			return
 		}
 		console.log('reloadWebsocket')
@@ -1146,11 +1138,7 @@
 				denoImportMap = buildDenoImportMap(await genAtaRoot($workspaceStore ?? ''), filePath)
 			}
 
-			const servers = lspServersFor({ editorLang: lang, scriptLang, denoImportMap })
-			if (servers.length === 0) {
-				closeWebsockets()
-			}
-			for (const server of servers) {
+			for (const server of lspServersFor({ editorLang: lang, scriptLang, denoImportMap })) {
 				await connectToLanguageServer(
 					server.url,
 					server.name,
@@ -1359,6 +1347,12 @@
 			if (!nmodel) {
 				throw err
 			}
+			// Headless linting creates models at this same canonical URI, so the existing
+			// one can hold whatever content was last linted. Show what this editor was
+			// given, not that.
+			if (nmodel.getValue() !== (code ?? '')) {
+				nmodel.setValue(code ?? '')
+			}
 			model = nmodel
 		}
 		model.updateOptions(lang == 'python' ? { tabSize: 4, insertSpaces: true } : updateOptions)
@@ -1620,8 +1614,8 @@
 				modelUri: uri,
 				absolutePathExtraLibs,
 				isCancelled: () => destroyed,
+				registerLocalModels: () => editor != undefined,
 				onLocalFileRegistered: () => {
-					if (!editor) return
 					try {
 						model?.setValue(model.getValue())
 					} catch (e) {
diff --git a/frontend/src/lib/components/copilot/chat/global/core.ts b/frontend/src/lib/components/copilot/chat/global/core.ts
index 71f4b5bc20..2b371b4b82 100644
--- a/frontend/src/lib/components/copilot/chat/global/core.ts
+++ b/frontend/src/lib/components/copilot/chat/global/core.ts
@@ -3832,7 +3832,7 @@ async function getLintErrors(args: LintTargetArgs, ctx: WriteDraftCtx): Promise<
 
 	let response = formatScriptLintResult(result)
 	if (result.unavailableServers?.length) {
-		response += `\n\nNote: the ${result.unavailableServers.join(' and ')} language server${result.unavailableServers.length > 1 ? 's were' : ' was'} unavailable, so some problems may not be listed. This usually means an editor is already open on a ${target.language} item.`
+		response += `\n\nNote: the ${result.unavailableServers.join(' and ')} language server${result.unavailableServers.length > 1 ? 's did' : ' did'} not respond, so some problems may not be listed. Treat a clean result as inconclusive.`
 	}
 	if (result.contentMismatch) {
 		response += `\n\nNote: an editor is currently open on this code and its buffer differs from the draft. The results above are for what that editor shows.`
diff --git a/frontend/src/lib/components/lint/headlessLint.ts b/frontend/src/lib/components/lint/headlessLint.ts
index f9be64fd3e..6e7eb4ef35 100644
--- a/frontend/src/lib/components/lint/headlessLint.ts
+++ b/frontend/src/lib/components/lint/headlessLint.ts
@@ -47,8 +47,7 @@ export interface HeadlessLintOutcome extends ScriptLintResult {
 	unavailableServers?: string[]
 }
 
-// Models we created ourselves, oldest first. An editor may later adopt one by URI, so
-// eviction must never dispose a model that is attached to an editor.
+// Models we created ourselves, least recently used first.
 const ownedModels: string[] = []
 const MAX_OWNED_MODELS = 4
 
@@ -56,11 +55,29 @@ const absolutePathExtraLibs = new Map<string, { dispose: () => void }>()
 const ataByKey = new Map<string, (source: string) => Promise<void>>()
 const pendingByUri = new Map<string, Promise<HeadlessLintOutcome>>()
 
+function withDeadline(promise: Promise<unknown>, ms: number): Promise<unknown> {
+	return Promise.race([promise, new Promise((resolve) => setTimeout(resolve, ms))])
+}
+
+function touchOwnedModel(uriString: string) {
+	const at = ownedModels.indexOf(uriString)
+	if (at >= 0) ownedModels.splice(at, 1)
+	ownedModels.push(uriString)
+}
+
 function evictOwnedModels(keepUri: string) {
 	while (ownedModels.length > MAX_OWNED_MODELS) {
 		const candidate = ownedModels.shift()
-		if (!candidate || candidate === keepUri) continue
+		if (!candidate) continue
+		if (candidate === keepUri) {
+			// Still in use: keep tracking it, or a later lint would mistake it for a model
+			// owned by an editor and refuse to update its content.
+			ownedModels.push(candidate)
+			continue
+		}
 		const model = meditor.getModel(Uri.parse(candidate))
+		// An editor may have adopted it in the meantime; disposing it would close the
+		// user's buffer.
 		if (model && !model.isAttachedToEditor()) {
 			model.dispose()
 		}
@@ -127,32 +144,41 @@ async function lintOne(
 	let model = meditor.getModel(uri)
 	let contentMismatch = false
 	if (model) {
-		const isOurs = ownedModels.includes(uriString)
-		if (isOurs) {
-			if (model.getValue() !== req.content) model.setValue(req.content)
-		} else {
-			// An editor owns this model: its content is what the user sees and what they would
-			// see the markers for. Lint it as-is rather than overwriting their buffer.
+		// Attachment decides, not who created it: an editor can adopt a model we made, and
+		// its buffer is what the user sees and would save. Never write to it.
+		if (model.isAttachedToEditor() || !ownedModels.includes(uriString)) {
 			contentMismatch = model.getValue() !== req.content
+		} else if (model.getValue() !== req.content) {
+			model.setValue(req.content)
+			// Markers from the previous content survive until revalidation finishes, and a
+			// matching marker count would let the wait below settle on them.
+			meditor.setModelMarkers(model, editorLang, [])
+			touchOwnedModel(uriString)
 		}
 	} else {
 		model = meditor.createModel(req.content, editorLang, uri)
-		ownedModels.push(uriString)
+		touchOwnedModel(uriString)
 		evictOwnedModels(uriString)
 	}
 
+	// Bounded: these fetch over the network, and lints of one URI are serialized behind
+	// each other, so one hung request would wedge the tool for that item indefinitely.
 	if (editorLang === 'typescript') {
-		await Promise.all([
-			ensureResourceTypeNamespace(req.workspace, req.scriptLang).catch((e) =>
-				console.error('headlessLint: resource types unavailable', e)
-			),
-			ensureCustomWmillTypes(req.workspace).catch(() => undefined)
-		])
+		await withDeadline(
+			Promise.all([
+				ensureResourceTypeNamespace(req.workspace, req.scriptLang),
+				ensureCustomWmillTypes(req.workspace)
+			]).catch((e) => console.error('headlessLint: extra libs unavailable', e)),
+			timeoutMs
+		)
 	}
 
 	if (req.scriptLang === 'bun' || req.scriptLang === 'bunnative') {
-		await acquireTypes(req, uriString).catch((e) =>
-			console.error('headlessLint: type acquisition failed', e)
+		await withDeadline(
+			acquireTypes(req, uriString).catch((e) =>
+				console.error('headlessLint: type acquisition failed', e)
+			),
+			timeoutMs
 		)
 	}
 
@@ -164,6 +190,11 @@ async function acquireTypes(req: HeadlessLintRequest, uriString: string): Promis
 	const key = `${req.workspace}:${uriString}`
 	let ata = ataByKey.get(key)
 	if (!ata) {
+		while (ataByKey.size >= MAX_OWNED_MODELS) {
+			const oldest = ataByKey.keys().next().value
+			if (oldest === undefined) break
+			ataByKey.delete(oldest)
+		}
 		ata = await createWindmillAta({
 			root: await genAtaRoot(req.workspace),
 			scriptPath: req.path,
@@ -214,15 +245,16 @@ async function countExpectedMarkers(uri: Uri, editorLang: string): Promise<numbe
 	}
 }
 
-// The editor's own lint paths sleep a fixed delay and hope. Instead, ask the worker how
-// many diagnostics it has and wait for that many markers to be published — which also
-// terminates promptly for clean code, where no marker-change event ever fires.
+// Ask the worker how many diagnostics it has and wait for that many markers to be
+// published. Clean code never fires a marker-change event, so there is no event to wait
+// on and a count is the only signal that validation has actually run.
 async function waitForMarkersToSettle(uri: Uri, editorLang: string, timeoutMs: number) {
 	const expected = await countExpectedMarkers(uri, editorLang)
+	if (expected === undefined) return
 	const deadline = Date.now() + timeoutMs
 	while (Date.now() < deadline) {
 		const published = meditor.getModelMarkers({ resource: uri, owner: editorLang }).length
-		if (expected !== undefined && published === expected) return
+		if (published === expected) return
 		await new Promise((r) => setTimeout(r, 50))
 	}
 }
diff --git a/frontend/src/lib/components/lint/headlessLsp.ts b/frontend/src/lib/components/lint/headlessLsp.ts
index 2e06da1c12..3e709b4140 100644
--- a/frontend/src/lib/components/lint/headlessLsp.ts
+++ b/frontend/src/lib/components/lint/headlessLsp.ts
@@ -57,12 +57,20 @@ function startClient(
 	return new Promise((resolve) => {
 		let settled = false
 		let webSocket: WebSocket
+		let client: MonacoLanguageClient | undefined
 
 		const finish = (v: StartedClient | undefined) => {
-			if (settled) return
+			if (settled) {
+				// The deadline already gave up on this client. Stop it, or it keeps holding
+				// the global command names it registered and every later lint of this
+				// language reports the server as unavailable.
+				if (v) void stopClient(v)
+				return
+			}
 			settled = true
 			clearTimeout(timer)
 			if (!v) {
+				if (client) void stopClient({ server, client, webSocket, pushedDiagnostics: Promise.resolve() })
 				try {
 					webSocket?.close()
 				} catch {}
@@ -93,7 +101,7 @@ function startClient(
 			let resolvePushed: () => void = () => {}
 			const pushedDiagnostics = new Promise<void>((r) => (resolvePushed = r))
 
-			const client = new MonacoLanguageClient({
+			client = new MonacoLanguageClient({
 				name: `headless-${server.name}`,
 				messageTransports: { reader, writer },
 				clientOptions: {
@@ -226,17 +234,16 @@ export async function lintWithLsp(req: {
 }): Promise<LspLintResult> {
 	await initializeVscode('headlessLsp')
 
-	const uriString = computeModelUri(
-		computeModelPath(undefined, req.scriptLang),
-		req.scriptLang,
-		req.editorLang
-	)
+	const modelPath = computeModelPath(undefined, req.scriptLang)
+	const uriString = computeModelUri(modelPath, req.scriptLang, req.editorLang)
 	const uri = Uri.parse(uriString)
 	const model = meditor.createModel(req.content, req.editorLang, uri)
 
+	// Built from where the document actually lives, not the workspace path: the map's
+	// relative entries are derived from the document's own depth.
 	const denoImportMap =
 		req.scriptLang === 'deno'
-			? buildDenoImportMap(await genAtaRoot(req.workspace), req.path)
+			? buildDenoImportMap(await genAtaRoot(req.workspace), modelPath)
 			: undefined
 	const servers = lspServersFor({
 		editorLang: req.editorLang,
@@ -257,29 +264,40 @@ export async function lintWithLsp(req: {
 			)
 		}
 
-		// A server is done when it has answered the diagnostic request. If it answers with
-		// nothing it may be a publisher instead, so give its push a bounded chance rather
-		// than concluding the document is clean.
-		const pulled = await withDeadline(
-			Promise.all(
-				started.map(async (s) => {
-					const items = await pullDiagnostics(s, uri)
-					if (items.length === 0) {
-						await withDeadline(s.pushedDiagnostics, PUSH_FALLBACK_MS, undefined)
-					}
-					return items
-				})
-			).then((r) => r.flat()),
-			timeoutMs,
-			[] as meditor.IMarker[]
+		// Each server is awaited on its own deadline: one that stalls must not discard
+		// what the others already reported, and must be named rather than counted as
+		// having found nothing.
+		const stalled: string[] = []
+		const perServer = await Promise.all(
+			started.map(async (s) => {
+				const items = await withDeadline(
+					(async () => {
+						const pulled = await pullDiagnostics(s, uri)
+						// A server that answers with nothing may be a publisher instead, so give
+						// its push a bounded chance before concluding the document is clean.
+						if (pulled.length === 0) {
+							await withDeadline(s.pushedDiagnostics, PUSH_FALLBACK_MS, undefined)
+						}
+						return pulled
+					})(),
+					timeoutMs,
+					undefined
+				)
+				if (items === undefined) {
+					stalled.push(s.server.name)
+					return []
+				}
+				return items
+			})
 		)
 
 		// Pushed diagnostics have already been turned into markers on the model.
 		const pushedMarkers = meditor.getModelMarkers({ resource: uri })
-		const unavailableServers = servers
-			.filter((s) => !started.some((st) => st.server.name === s.name))
-			.map((s) => s.name)
-		return { ...dedupe([...pushedMarkers, ...pulled]), unavailableServers }
+		const unavailableServers = [
+			...servers.filter((s) => !started.some((st) => st.server.name === s.name)).map((s) => s.name),
+			...stalled
+		]
+		return { ...dedupe([...pushedMarkers, ...perServer.flat()]), unavailableServers }
 	} finally {
 		await Promise.all(started.map(stopClient))
 		model.dispose()
diff --git a/frontend/src/lib/components/lint/lspLanguageConfig.ts b/frontend/src/lib/components/lint/lspLanguageConfig.ts
index 23fccc09be..138efd3999 100644
--- a/frontend/src/lib/components/lint/lspLanguageConfig.ts
+++ b/frontend/src/lib/components/lint/lspLanguageConfig.ts
@@ -11,7 +11,7 @@ export interface LspServerConfig {
 	middleware?: (params: any, token: any, next: any) => any
 }
 
-export function lspLanguagesFor(editorLang: string, scriptLang: string | undefined): boolean {
+export function hasLanguageServers(editorLang: string, scriptLang: string | undefined): boolean {
 	return (
 		(editorLang === 'typescript' && scriptLang === 'deno') ||
 		editorLang === 'python' ||
diff --git a/frontend/src/lib/components/lint/typescriptAta.ts b/frontend/src/lib/components/lint/typescriptAta.ts
index a868ac5608..078ec9922b 100644
--- a/frontend/src/lib/components/lint/typescriptAta.ts
+++ b/frontend/src/lib/components/lint/typescriptAta.ts
@@ -36,6 +36,8 @@ export interface WindmillAtaOptions {
 	modelUri: string
 	absolutePathExtraLibs: Map<string, { dispose: () => void }>
 	isCancelled?: () => boolean
+	/** Whether relative-import files should be materialized as Monaco models. */
+	registerLocalModels?: () => boolean
 	/** Called after a relative-import model is registered, to nudge revalidation. */
 	onLocalFileRegistered?: () => void
 }
@@ -67,13 +69,15 @@ export async function createWindmillAta(
 			opts.absolutePathExtraLibs.get(_path)?.dispose()
 			opts.absolutePathExtraLibs.set(_path, typescriptDefaults.addExtraLib(code, _path))
 		}
-		const localModel = meditor.getModel(nuri)
-		if (localModel) {
-			localModel.setValue(code)
-		} else {
-			meditor.createModel(code, 'typescript', nuri)
+		if (opts.registerLocalModels?.() ?? true) {
+			const localModel = meditor.getModel(nuri)
+			if (localModel) {
+				localModel.setValue(code)
+			} else {
+				meditor.createModel(code, 'typescript', nuri)
+			}
+			opts.onLocalFileRegistered?.()
 		}
-		opts.onLocalFileRegistered?.()
 	}
 
 	await initWasmTs()
diff --git a/frontend/src/lib/components/lint/typescriptExtraLibs.ts b/frontend/src/lib/components/lint/typescriptExtraLibs.ts
index 0eea42dc8c..6f348d68de 100644
--- a/frontend/src/lib/components/lint/typescriptExtraLibs.ts
+++ b/frontend/src/lib/components/lint/typescriptExtraLibs.ts
@@ -59,6 +59,6 @@ export function applyCustomWmillTypes(data: CustomWmillTypesData): () => void {
 	}
 }
 
-export async function ensureCustomWmillTypes(workspace: string): Promise<() => void> {
-	return applyCustomWmillTypes(await fetchCustomWmillTypesData(workspace))
+export async function ensureCustomWmillTypes(workspace: string): Promise<void> {
+	applyCustomWmillTypes(await fetchCustomWmillTypesData(workspace))
 }